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History of OP-20-GU (Coast Guard Cryptanalytic Unit)

by: National Archives and Records Administration

Publication date: 1943-10-16

Usage: Public Domain Mark 1.0

Topics: U.S. Coast Guard, OP-20-GU, U.S. Navy, OP-20-G, FBI, codebreaking, cryptanalysis, intelligence, counterintelligence, Elizebeth Friedman, Leonard Jones, clandestine, Nazi, WWII

Collection: elf_codebreaker; additional_collections

Language: English

Narrative history of the U.S. Coast Guard Cryptanalytic Unit (a.k.a. Unit 387), written by Lt. Leonard T. Jones in October 1943. Describes the unit’s founding in 1931 by Elizebeth Smith Friedman and its evolution through Prohibition and into WWII, when the unit was incorporated into Navy intelligence and renamed OP-20-GU. This history is noteworthy because it describes in detail the codebreaking work that the Coast Guard did on behalf of the FBI. It also expresses frustration over the FBI’s "much too free use" of verbatim decrypts provided by the Coast Guard, and criticizes the Bureau's handling of Nazi spies in Brazil during an incident in March 1942.

NARA location: RG 38, CNSG Library, box 115, 5750/193.